The US and Cameroon, as well as the other five countries in the CEMAC zone, including Central African Republic, Chad, Equatorial Guinea, Gabon, and the Republic of the Congo.
Note that if you live in the US or Cameroon you can set up a Kappa account and send or receive money between the two countries. You can also send and receive money within Cameroon as well as to businesses and individuals in the CEMAC zone. Businesses and individuals in other CEMAC countries cannot set up an account yet. Kappa aims to increase coverage to other countries.